The Natural History and Morphology of Dero vaga

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266 THE AMERICAN NATURALIST. [Vol. XXXIII.

and the description of the membrana tectoria as a cuticular structure
(p. 890), may be contrary to fact, but they are blemishes which dis-
appear in the marvelous wealth of accurate information which fills
the whole work.

The place that the new Anatomy will find is not difficult to predict.
Its size and fullness, together with the heaviness of Gegenbaur's style,
will probably prevent it from being a popular text-book with most
beginners, but its masterly qualities will make it an absolute neces-
sity to every advanced student of vertebrate anatomy. In this
respect it will occupy the field formerly held by Wiedersheim's
Lehrbuch, though it seems to us unlikely that it will replace in any
extensive way this author's Grundriss, which from its elementary
character and simple language makes so satisfactory a book for
the beginner.

The heavy debt which vertebrate anatomists already owe to Gegen-
baur is materially increased by this accession to the list of best text-
books, and it must be the wish of every one that circumstances may
favor the early completion of a work destined to be so scholarly and
valuable a contribution to the comparative anatomy of the verte-
brates. G H P

The Natural History and Morphology of Dero vaga. 1 — This
interesting little aquatic worm was described twenty years ago by
Dr. Joseph Leidy 2 in this journal as Aulophorus vagus. It is found
in shady places among vegetation in ponds and ditches, living by
preference among masses of floating Lemna or among algae on the
bottom, shifting its position gradually from surface to bottom or
vice versa, according to the location of food supply. Its food consists
of vegetable matter, principally desmids, algas, and even the fronds
of Lemna. The worms inhabit cases which they construct of stato-
blasts, Arcella shells, the leaves of Lemna, etc. The cases of indi-
viduals living at the surface float, and those of individuals living at
the bottom sink when the worms are removed. The period of
sexual reproduction occurs during the first two weeks of July, when
the body cavity posterior to the clitellum is crowded with eggs.
Asexual reproduction by fission takes place throughout the year, but
most rapidly during warm weather, when it may occur as often as

1 Brode, H. S. A Contribution to the Morphology of Dero vaga, Journ. of
Morph., vol. xiv (1898), pp. 141-180, Pis. XIII-XVI.

2 Leidy, J. Notice of Some Aquatic Worms of the Family Naids, Am. Nat.,
vol. xiv (1880), pp. 421-425.

No. 387.] REVIEWS OF RECENT LITERATURE. 267

three times a week. Three fission zones have been observed in one
individual at the same time. As the animal grows in length, the
case which it inhabits is extended, and after fission the two daughter-
worms divide it by placing their heads together at its middle and
forcibly breaking it ; each worm then swims away with one-half of
the old case. The fission zone is formed near the middle of some
segment, usually back of XVII and in front of XXII. The new
head and tail are almost completely formed before separation takes
place. The number of somites in the new head is constant, being
five, while twelve to sixteen segments are visible in the tail before a
second fission begins. Worms divided by cutting regenerate the miss-
ing part, though only enough segments are regenerated at the ante-
rior end to complete the cephalized portion, i.e., the first five. Thus
if two are removed but two regenerate, while if seven are taken away
only five new segments are formed. At least three or four segments
in addition to the five in the cephalic region are necessary for the
regeneration of the tail. Dr. Erode gives a detailed account of the
structure of the body wall, of the nervous system, and of the sense
organs. Each segment is provided with four lateral nerves which
arise from the ventral ganglion and pass to the body wall and thence
dorsally. The epidermis is provided with a remarkable series of
sense organs, each segment bearing two series arranged in greater
and lesser circular bands of twelve and eight organs respectively.
These organs are so spaced as to form twenty longitudinal rows
extending the whole length of the body. Dr. Erode also confirms
Hesse's view that the so-called lateral line of oligochetes is formed
by the accumulation of the nucleated plasma portions of the circular
muscle fibres and cannot, therefore, be interpreted as a nervous struc-
ture. The epidermal sense organs have no share in the formation of
this line. The marked serial symmetry of the epidermal sense organs
and lateral nerves is held by the author to support the colonial
theory of the origin of metamerism. C A K

Crustacea of Florida and the Bahamas. — Miss Mary J. Rath-
bun is an indefatigable student of Crustacea. In fact, the mantles
of Stimpson, Smith, Kingsley, Say, Gill, Gibbes, and all other past
students of the group appear to have fallen on her shoulders. In
the paper before us she describes the 127 species of brachyma, col-
lected by the Iowa University Expedition of 1893. 1 Several new

1 Bulletin of the Laboratories of Natural History of Iowa University, June,
189S.